Import smallvec-1.4.0 am: ddfee16c0a am: e42445152a am: ef31f8c504

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/smallvec/+/1374113

Change-Id: Ib307b787bed73d15e5190f406c707cc3fb9d5488